1. Field of the Invention
This invention relates to alertness detection systems and more particularly to a system to detect alertness or consciousness activity by eyelid movement.
2. Description of the Prior Art
Various mechanical and electrical devices have been tried in order to warn an individual that he is becoming drowsy, but none has been shown to be of practical or commercial value. If viable, such devices would be useful for drivers to prevent loss of alertness and sleeping at the wheel, a cause of many accidents.
For instance, one electronic safety alarm consists of a lightweight plastic device which coils around the person's ear and sounds a buzzer when his head nods. The disadvantages of such a device are that mental alertness is lost long before an individual's head nods, and the device can be falsely triggered when the individual moves his head voluntarily.
Another example of a warning device is a button steering wheel alarm which must be continually depressed in order to keep the alarm from sounding. Similar to this steering wheel button is a foot pedal which requires the individual to hold a button down with his left foot while driving or operating other machinery. However, these devices would sound the alarm falsely when the hands and feet were used to operate the automobile or other machinery. Further, they rely on the assumption that less pressure or force is applied to the controls as the degree of alertness of the operator decreases, an assumption that is subject to dispute.
Other devices have employed the detection and measurement of physiological data to detect the state of drowsiness. A device used in the laboratory, the electroencephalograph (eeg), has been an effective way of monitoring alertness in an individual. This device plots brain voltages against time but, because the wave form obtained is not necessarily a periodic function, the device is of limited usefulness. Furthermore, these voltages are of extremely low amplitude and require recording apparatus which displays excellent noise rejection characteristics. Also, this device fails in practical applications since it is not small, light, easy to adjust, simple to operate or easy to maintain. Although portable alpha wave machines are available, the range of individual differences in the amount and frequency of alpha rhythm patterns is significant and relatively independent of alertness, and in addition some normal people do not exhibit an alpha rhythm.
Attempts have been made to measure tension of the supraorbital muscles and to correlate this muscle tension directly with alertness. Bipolar electrodes were placed over the supraorbital regions of an individual to sense muscle tension. These attempts encountered technical problems for various reasons. Even the portable model was quite sizable and heavy. Furthermore there was AC line interference whenever it was removed from the laboratory, and there was a high noise level of the amplification system.
Thus, there has been a failure to provide a reliable system to detect reduction in alertness at an early stage of the drowsiness sequence. Further, the devices that have attempted to detect drowsiness have been bulky, heavy, unreliable, unable to discriminate against noise interference, not easy to maintain, and not suitable of being used by a wide range of individuals.